In medical endoscopes such as nasal endoscopes or the like, there has been a demand in recent years for reducing the size of a tip of an inserted portion thereof from the viewpoint of reducing the burden on patients or the like. In response, small image-acquisition devices (CCDs, and CMOSs) have been developed for endoscopes, and the pixel pitch thereof is also decreasing year by year. Associated with this decrease in the pixel pitch, allowable assembly errors between individual lenses, between an image-acquisition device and an objective lens, and so forth are also decreasing, and thus, assembly errors of several micrometers are becoming problematic.
As disclosed in Patent Literature 1, an endoscope image-acquisition unit has a structure in which an objective-lens-unit frame that holds an objective lens and an image-acquisition-device holding frame that holds an image-acquisition device are fitted together. More specifically, thermosetting resin is filled in fitting portions between the objective-lens-unit frame and the image-acquisition-device holding frame, and, after the positions of an objective optical system and the image-acquisition device are set, the objective-lens-unit frame and the image-acquisition-device holding frame are secured by using assembly jigs and are placed in a drying oven or the like in this state to be heated. By doing so, the thermosetting resin is hardened, thus attaching and securing the objective-lens-unit frame to the image-acquisition-device holding frame.